This present application relates generally to methods, systems, and/or apparatus for improving the operation of steam turbine engines. More specifically, but not by way of limitation, the present application relates to improved methods, systems, and/or apparatus pertaining to the operation of steam turbines with 3-flow low pressure turbines.
As one of ordinary skill in the art will appreciate, steam turbine plants may be constructed with a rotor train that, via a common shaft, connects multiple turbines that operate at varying pressure levels. Typically, each of these turbines is paired with another turbine so that the axial thrust force (or “thrust”) being exerted on the shaft by each may be balanced by another. For example, a steam turbine plant may include a high-pressure turbine that is paired with an intermediate-pressure turbine. During operation, these turbines may be configured so that the thrust force each applies to the shaft is offset (or substantially offset) by the thrust the other applies. In addition, steam turbine plants often have two low-pressure turbines that are paired with each other in the same manner, i.e., so that the thrust each applies to the shaft balances the thrust of the other.
In some cases, however, the thrust forces applied across a rotor train having a common shaft cannot be balanced by pairing turbines. It will be understood that, in such situations, large, expensive thrust bearings generally are required to provide the counteracting forces so that thrust balance is achieved. In some applications, having an odd number of turbines would be advantageous, particularly where one of the turbines could be activated and deactivated depending on load requirements. In this case, the odd number of turbines and/or the fact that one is operated only at peak load periods means thrust balancing would be impossible by simply pairing the turbines to offset similar thrust forces. This system, instead, would have to include a sizable thrust bearing to counteract the force of generated by the part-time turbine when it operated. This solution, however, is not desirable because the cost of constructing and maintaining the thrust bearing is considerable, a fact that is even less palatable considering the thrust bearing is only needed on a pan-time basis, i.e., when the part-time turbine is activated.
As a result, there is a need for improved systems and/or apparatus for balancing rotor thrust in changing operating conditions and, for rotor trains that are difficult to balance because of the varying turbine size and number, particularly where the improvements are cost-effective and simple in both construction and operation.